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feat(services/pam): Do not expose internal errors to client #420

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feat(services/pam): Do not expose internal errors to client #420

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46 changes: 45 additions & 1 deletion internal/services/pam/pam.go
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@ import (
"encoding/json"
"errors"
"fmt"
"log/slog"
"os/user"

"github.com/ubuntu/authd"
Expand Down Expand Up @@ -58,7 +59,9 @@ func (s Service) AvailableBrokers(ctx context.Context, _ *authd.Empty) (*authd.A

// GetPreviousBroker returns the previous broker set for a given user, if any.
// If the user is not in our cache, it will try to check if it’s on the system, and return then "local".
func (s Service) GetPreviousBroker(ctx context.Context, req *authd.GPBRequest) (*authd.GPBResponse, error) {
func (s Service) GetPreviousBroker(ctx context.Context, req *authd.GPBRequest) (gpbr *authd.GPBResponse, err error) {
defer redactError(&err)

// Use in memory cache first
if b := s.brokerManager.BrokerForUser(req.GetUsername()); b != nil {
return &authd.GPBResponse{PreviousBroker: b.ID}, nil
Expand Down Expand Up @@ -101,6 +104,7 @@ func (s Service) GetPreviousBroker(ctx context.Context, req *authd.GPBRequest) (

// SelectBroker starts a new session and selects the requested broker for the user.
func (s Service) SelectBroker(ctx context.Context, req *authd.SBRequest) (resp *authd.SBResponse, err error) {
defer redactError(&err)
defer decorate.OnError(&err, "can't start authentication transaction")

username := req.GetUsername()
Expand Down Expand Up @@ -141,6 +145,7 @@ func (s Service) SelectBroker(ctx context.Context, req *authd.SBRequest) (resp *

// GetAuthenticationModes fetches a list of authentication modes supported by the broker depending on the session information.
func (s Service) GetAuthenticationModes(ctx context.Context, req *authd.GAMRequest) (resp *authd.GAMResponse, err error) {
defer redactError(&err)
defer decorate.OnError(&err, "could not get authentication modes")

sessionID := req.GetSessionId()
Expand Down Expand Up @@ -182,6 +187,7 @@ func (s Service) GetAuthenticationModes(ctx context.Context, req *authd.GAMReque

// SelectAuthenticationMode set given authentication mode as selected for this sessionID to the broker.
func (s Service) SelectAuthenticationMode(ctx context.Context, req *authd.SAMRequest) (resp *authd.SAMResponse, err error) {
defer redactError(&err)
defer decorate.OnError(&err, "can't select authentication mode")

sessionID := req.GetSessionId()
Expand Down Expand Up @@ -211,6 +217,7 @@ func (s Service) SelectAuthenticationMode(ctx context.Context, req *authd.SAMReq

// IsAuthenticated returns broker answer to authentication request.
func (s Service) IsAuthenticated(ctx context.Context, req *authd.IARequest) (resp *authd.IAResponse, err error) {
defer redactError(&err)
defer decorate.OnError(&err, "can't check authentication")

sessionID := req.GetSessionId()
Expand Down Expand Up @@ -248,6 +255,7 @@ func (s Service) IsAuthenticated(ctx context.Context, req *authd.IARequest) (res
data = ""
}

data = redactMessage(data)
return &authd.IAResponse{
Access: access,
Msg: data,
Expand All @@ -256,6 +264,7 @@ func (s Service) IsAuthenticated(ctx context.Context, req *authd.IARequest) (res

// SetDefaultBrokerForUser sets the default broker for the given user.
func (s Service) SetDefaultBrokerForUser(ctx context.Context, req *authd.SDBFURequest) (empty *authd.Empty, err error) {
defer redactError(&err)
defer decorate.OnError(&err, "can't set default broker %q for user %q", req.GetBrokerId(), req.GetUsername())

if req.GetUsername() == "" {
Expand All @@ -279,6 +288,7 @@ func (s Service) SetDefaultBrokerForUser(ctx context.Context, req *authd.SDBFURe

// EndSession asks the broker associated with the sessionID to end the session.
func (s Service) EndSession(ctx context.Context, req *authd.ESRequest) (empty *authd.Empty, err error) {
defer redactError(&err)
defer decorate.OnError(&err, "could not abort session")

sessionID := req.GetSessionId()
Expand Down Expand Up @@ -335,3 +345,37 @@ func mapToUILayout(layout map[string]string) (r *authd.UILayout) {
Code: &code,
}
}

// errGeneric is the error to return when the broker returns an error.
//
// This error is returned to the client to prevent information leaks.
var errGeneric = errors.New("authentication failure")

// redactError replaces the error with a generic one to prevent information leaks.
//
// Since the error messages contain useful information for debugging, the original error message
// is written in the system logs.
func redactError(err *error) {
if *err == nil {
return
}
slog.Debug(fmt.Sprintf("%v", err))
*err = errGeneric
}
Comment on lines +358 to +364
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So, from my POV this is a bit too agrressive, since it's also changing the messages that the broker wants us to write with a generic "authentication failure".

While things such as invalid password 'really, it's not a goodpass!', should be 'goodpass' which are the broker auth messages should be exposed by the UI as they are.

Not sure what's the best way to filter them though. But ideally it's up to the broker not to send private details as Authentication message, while it may indeed provide more useful information for other kind of failures (for example on time out, or when something requires an user action).

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@denisonbarbosa denisonbarbosa Jul 16, 2024 •
edited

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I agree and disagree also. I agree that this is indeed aggressive, but that's what other PAM modules tend to do as well to avoid leaking anything that could potentially be used by an attacker.

Also, the whole point of authd is to be a layer between 3rd party brokers and the machine. It's our business logic to ensure that what we show the user is what can be shown. Expecting the brokers to respect and match what we do locally defeats part of the purpose.


// genericErrorMessage is the message to return when the broker returns an error message.
//
// This message is returned to the client to prevent information leaks.
const genericErrorMessage string = `{"message":"authentication failure"}`

// redactMessage replaces the message with a generic one to prevent information leaks.
//
// Since the message contains useful information for debugging, the original message is written
// in the system logs.
func redactMessage(msg string) string {
if msg == "{}" || msg == "" {
return msg
}
slog.Debug(fmt.Sprintf("Got broker message: %q", msg))
return genericErrorMessage
}
2 changes: 1 addition & 1 deletion ...ta/TestIsAuthenticated/golden/denies_authentication_when_broker_times_out/IsAuthenticated
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@@ -1,4 +1,4 @@
FIRST CALL:
access: denied
msg: {"message": "denied by time out"}
msg: {"message":"authentication failure"}
err: <nil>
2 changes: 1 addition & 1 deletion ...m/testdata/TestIsAuthenticated/golden/error_on_empty_data_even_if_granted/IsAuthenticated
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@@ -1,4 +1,4 @@
FIRST CALL:
access:
msg:
err: rpc error: code = Unknown desc = can't check authentication: missing key "userinfo" in returned message, got: {}
err: rpc error: code = Unknown desc = authentication failure
2 changes: 1 addition & 1 deletion ...sAuthenticated/golden/error_on_updating_local_groups_with_unexisting_file/IsAuthenticated
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@@ -1,4 +1,4 @@
FIRST CALL:
access:
msg:
err: rpc error: code = Unknown desc = can't check authentication: failed to update user "TestIsAuthenticated/Error_on_updating_local_groups_with_unexisting_file_separator_success_with_local_groups": could not update local groups for user "TestIsAuthenticated/Error_on_updating_local_groups_with_unexisting_file_separator_success_with_local_groups": could not fetch existing local group: open testdata/TestIsAuthenticated/does_not_exists.group: no such file or directory
err: rpc error: code = Unknown desc = authentication failure
2 changes: 1 addition & 1 deletion ...ervices/pam/testdata/TestIsAuthenticated/golden/error_when_authenticating/IsAuthenticated
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@@ -1,4 +1,4 @@
FIRST CALL:
access:
msg:
err: rpc error: code = Unknown desc = can't check authentication: broker "BrokerMock": IsAuthenticated errored out
err: rpc error: code = Unknown desc = authentication failure
2 changes: 1 addition & 1 deletion ...tdata/TestIsAuthenticated/golden/error_when_broker_returns_invalid_access/IsAuthenticated
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
FIRST CALL:
access:
msg:
err: rpc error: code = Unknown desc = can't check authentication: invalid access authentication key: invalid
err: rpc error: code = Unknown desc = authentication failure
3 changes: 1 addition & 2 deletions ...estdata/TestIsAuthenticated/golden/error_when_broker_returns_invalid_data/IsAuthenticated
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Original file line number Diff line number Diff line change
@@ -1,5 +1,4 @@
FIRST CALL:
access:
msg:
err: rpc error: code = Unknown desc = can't check authentication: response returned by the broker is not a valid json: invalid character 'i' looking for beginning of value
Broker returned: invalid
err: rpc error: code = Unknown desc = authentication failure
2 changes: 1 addition & 1 deletion ...ata/TestIsAuthenticated/golden/error_when_broker_returns_invalid_userinfo/IsAuthenticated
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@@ -1,4 +1,4 @@
FIRST CALL:
access:
msg:
err: rpc error: code = Unknown desc = can't check authentication: message is not JSON formatted: json: cannot unmarshal string into Go value of type brokers.userInfo
err: rpc error: code = Unknown desc = authentication failure
2 changes: 1 addition & 1 deletion ...golden/error_when_broker_returns_username_different_than_the_one_selected/IsAuthenticated
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
FIRST CALL:
access:
msg:
err: rpc error: code = Unknown desc = can't check authentication: provided userinfo is invalid: username "different_username" does not match the selected username "TestIsAuthenticated/Error_when_broker_returns_username_different_than_the_one_selected_separator_IA_info_mismatching_user_name"
err: rpc error: code = Unknown desc = authentication failure
2 changes: 1 addition & 1 deletion ...tIsAuthenticated/golden/error_when_calling_second_time_without_cancelling/IsAuthenticated
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Expand Up @@ -5,4 +5,4 @@ FIRST CALL:
SECOND CALL:
access:
msg:
err: rpc error: code = Unknown desc = can't check authentication: broker "BrokerMock": IsAuthenticated already running for session "TestIsAuthenticated/Error_when_calling_second_time_without_cancelling_separator_IA_second_call-session_id"
err: rpc error: code = Unknown desc = authentication failure
2 changes: 1 addition & 1 deletion ...ces/pam/testdata/TestIsAuthenticated/golden/error_when_sessionid_is_empty/IsAuthenticated
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
FIRST CALL:
access:
msg:
err: rpc error: code = InvalidArgument desc = can't check authentication: rpc error: code = InvalidArgument desc = no session ID provided
err: rpc error: code = Unknown desc = authentication failure
2 changes: 1 addition & 1 deletion ...ces/pam/testdata/TestIsAuthenticated/golden/error_when_there_is_no_broker/IsAuthenticated
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
FIRST CALL:
access:
msg:
err: rpc error: code = Unknown desc = can't check authentication: no broker found for session "invalid-session"
err: rpc error: code = Unknown desc = authentication failure
8 changes: 4 additions & 4 deletions pam/integration-tests/gdm_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -213,7 +213,7 @@ func TestGdmModule(t *testing.T) {
"Error on missing user": {
pamUser: ptrValue(""),
wantPamErrorMessages: []string{
"can't select broker: rpc error: code = InvalidArgument desc = can't start authentication transaction: rpc error: code = InvalidArgument desc = no user name provided",
"can't select broker: rpc error: code = Unknown desc = authentication failure",
},
wantError: pam.ErrSystem,
wantAcctMgmtErr: pam_test.ErrIgnore,
Expand Down Expand Up @@ -279,7 +279,7 @@ func TestGdmModule(t *testing.T) {
},
},
wantPamErrorMessages: []string{
"invalid password 'really, it's not a goodpass!', should be 'goodpass'",
"authentication failure",
},
wantError: pam.ErrAuth,
wantAcctMgmtErr: pam_test.ErrIgnore,
Expand All @@ -294,7 +294,7 @@ func TestGdmModule(t *testing.T) {
},
},
wantPamErrorMessages: []string{
"user not found",
"authentication failure",
},
wantError: pam.ErrAuth,
wantAcctMgmtErr: pam_test.ErrIgnore,
Expand All @@ -311,7 +311,7 @@ func TestGdmModule(t *testing.T) {
},
},
wantPamErrorMessages: []string{
fido1AuthID + " should have wait set to true",
"authentication failure",
},
wantError: pam.ErrAuth,
wantAcctMgmtErr: pam_test.ErrIgnore,
Expand Down
12 changes: 6 additions & 6 deletions ...ion-tests/testdata/TestCLIAuthenticate/golden/deny_authentication_if_max_attempts_reached
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Expand Up @@ -133,7 +133,7 @@ Gimme your password
> ./pam_authd login socket=${AUTHD_TESTS_CLI_AUTHENTICATE_TESTS_SOCK}
Gimme your password
>
invalid password 'wrongpass', should be 'goodpass'
authentication failure



Expand Down Expand Up @@ -166,7 +166,7 @@ invalid password 'wrongpass', should be 'goodpass'
> ./pam_authd login socket=${AUTHD_TESTS_CLI_AUTHENTICATE_TESTS_SOCK}
Gimme your password
>
invalid password 'wrongpass', should be 'goodpass'
authentication failure



Expand Down Expand Up @@ -199,7 +199,7 @@ invalid password 'wrongpass', should be 'goodpass'
> ./pam_authd login socket=${AUTHD_TESTS_CLI_AUTHENTICATE_TESTS_SOCK}
Gimme your password
>
invalid password 'wrongpass', should be 'goodpass'
authentication failure



Expand Down Expand Up @@ -232,7 +232,7 @@ invalid password 'wrongpass', should be 'goodpass'
> ./pam_authd login socket=${AUTHD_TESTS_CLI_AUTHENTICATE_TESTS_SOCK}
Gimme your password
>
invalid password 'wrongpass', should be 'goodpass'
authentication failure



Expand Down Expand Up @@ -265,7 +265,7 @@ invalid password 'wrongpass', should be 'goodpass'
> ./pam_authd login socket=${AUTHD_TESTS_CLI_AUTHENTICATE_TESTS_SOCK}
Gimme your password
>
PAM Error Message: invalid password 'wrongpass', should be 'goodpass'
PAM Error Message: authentication failure
PAM Authenticate() for user "user-integration-max-attempts" exited with error (PAM exit code: 7)
: Authentication failure
PAM Info Message: acct=incomplete
Expand Down Expand Up @@ -298,7 +298,7 @@ dispatch
> ./pam_authd login socket=${AUTHD_TESTS_CLI_AUTHENTICATE_TESTS_SOCK}
Gimme your password
>
PAM Error Message: invalid password 'wrongpass', should be 'goodpass'
PAM Error Message: authentication failure
PAM Authenticate() for user "user-integration-max-attempts" exited with error (PAM exit code: 7)
: Authentication failure
PAM Info Message: acct=incomplete
Expand Down
8 changes: 4 additions & 4 deletions ...tion-tests/testdata/TestCLIAuthenticate/golden/deny_authentication_if_user_does_not_exist
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Expand Up @@ -121,14 +121,14 @@ Username: user-unexistent



PAM Error Message: can't select broker: rpc error: code = Unknown desc = can't start authenticat
ion transaction: user "user-unexistent" does not exist
PAM Error Message: can't select broker: rpc error: code = Unknown desc = authentication failure
PAM Authenticate() for user "user-unexistent" exited with error (PAM exit code: 4): System error
PAM Info Message: acct=incomplete
PAM AcctMgmt() exited with error (PAM exit code: 25): The return value should be ignored by PAM
dispatch
>


────────────────────────────────────────────────────────────────────────────────
> ./pam_authd login socket=${AUTHD_TESTS_CLI_AUTHENTICATE_TESTS_SOCK}
Select your provider
Expand All @@ -154,12 +154,12 @@ dispatch



PAM Error Message: can't select broker: rpc error: code = Unknown desc = can't start authenticat
ion transaction: user "user-unexistent" does not exist
PAM Error Message: can't select broker: rpc error: code = Unknown desc = authentication failure
PAM Authenticate() for user "user-unexistent" exited with error (PAM exit code: 4): System error
PAM Info Message: acct=incomplete
PAM AcctMgmt() exited with error (PAM exit code: 25): The return value should be ignored by PAM
dispatch
>


────────────────────────────────────────────────────────────────────────────────
12 changes: 6 additions & 6 deletions ...ion-tests/testdata/TestCLIAuthenticate/golden/deny_authentication_if_usernames_dont_match
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Expand Up @@ -132,9 +132,8 @@ Gimme your password
────────────────────────────────────────────────────────────────────────────────
> ./pam_authd login socket=${AUTHD_TESTS_CLI_AUTHENTICATE_TESTS_SOCK}
Gimme your password
PAM Error Message: authentication status failure: rpc error: code = Unknown desc = can't check a
uthentication: provided userinfo is invalid: username "mismatching-username" does not match the
selected username "user-mismatching-name"
PAM Error Message: authentication status failure: rpc error: code = Unknown desc = authenticatio
n failure
PAM Authenticate() for user "user-mismatching-name" exited with error (PAM exit code: 4): System
error
PAM Info Message: acct=incomplete
Expand All @@ -160,14 +159,14 @@ dispatch






────────────────────────────────────────────────────────────────────────────────
> ./pam_authd login socket=${AUTHD_TESTS_CLI_AUTHENTICATE_TESTS_SOCK}
Gimme your password
PAM Error Message: authentication status failure: rpc error: code = Unknown desc = can't check a
uthentication: provided userinfo is invalid: username "mismatching-username" does not match the
selected username "user-mismatching-name"
PAM Error Message: authentication status failure: rpc error: code = Unknown desc = authenticatio
n failure
PAM Authenticate() for user "user-mismatching-name" exited with error (PAM exit code: 4): System
error
PAM Info Message: acct=incomplete
Expand All @@ -193,6 +192,7 @@ dispatch






────────────────────────────────────────────────────────────────────────────────
12 changes: 6 additions & 6 deletions ...egration-tests/testdata/TestCLIChangeAuthTok/golden/prevent_change_password_if_auth_fails
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Expand Up @@ -133,7 +133,7 @@ Gimme your password
> ./pam_authd passwd socket=${AUTHD_TESTS_CLI_AUTHTOK_TESTS_SOCK}
Gimme your password
>
invalid password 'wrongpass', should be 'goodpass'
authentication failure



Expand Down Expand Up @@ -166,7 +166,7 @@ invalid password 'wrongpass', should be 'goodpass'
> ./pam_authd passwd socket=${AUTHD_TESTS_CLI_AUTHTOK_TESTS_SOCK}
Gimme your password
>
invalid password 'wrongpass', should be 'goodpass'
authentication failure



Expand Down Expand Up @@ -199,7 +199,7 @@ invalid password 'wrongpass', should be 'goodpass'
> ./pam_authd passwd socket=${AUTHD_TESTS_CLI_AUTHTOK_TESTS_SOCK}
Gimme your password
>
invalid password 'wrongpass', should be 'goodpass'
authentication failure



Expand Down Expand Up @@ -232,7 +232,7 @@ invalid password 'wrongpass', should be 'goodpass'
> ./pam_authd passwd socket=${AUTHD_TESTS_CLI_AUTHTOK_TESTS_SOCK}
Gimme your password
>
invalid password 'wrongpass', should be 'goodpass'
authentication failure



Expand Down Expand Up @@ -265,7 +265,7 @@ invalid password 'wrongpass', should be 'goodpass'
> ./pam_authd passwd socket=${AUTHD_TESTS_CLI_AUTHTOK_TESTS_SOCK}
Gimme your password
>
PAM Error Message: invalid password 'wrongpass', should be 'goodpass'
PAM Error Message: authentication failure
PAM ChangeAuthTok() for user "user-integration-max-attempts" exited with error (PAM exit code: 7
): Authentication failure
PAM Info Message: acct=incomplete
Expand Down Expand Up @@ -298,7 +298,7 @@ dispatch
> ./pam_authd passwd socket=${AUTHD_TESTS_CLI_AUTHTOK_TESTS_SOCK}
Gimme your password
>
PAM Error Message: invalid password 'wrongpass', should be 'goodpass'
PAM Error Message: authentication failure
PAM ChangeAuthTok() for user "user-integration-max-attempts" exited with error (PAM exit code: 7
): Authentication failure
PAM Info Message: acct=incomplete
Expand Down